Defense Technology International - March 2007 - (Page 12)
TECH WATCH RON LAURENZO EYE WIDE OPEN Darpa seeks to enhance the
capabilities of persistent surveillance by combining one of aviation’s
oldest technologies, the airship, with the latest in electronic detection,
the world’s largest active electronically scanned array radar. The
program behind this, ISIS Integrated Sensor Is Structure , aims to develop
technologies that allow one platform to provide continuous ground and
aerial radar scanning for up to 10 years. The heart of the system will be
a huge AESA radar bonded to the interior of an airship. The competition t
o design the airship is between L o c k h e e d Martin Skunk Works, w h i
c h proposes a cigar-shaped structure, and Northrop Grumman Electronic
Systems, which is working on a saucer concept. Aside from the radar, the
heaviest thing on ISIS will be its skin, which is being developed by
Lockheed Martin MS2 Defense and Surveillance Systems. The large-aperture,
low-powerdensity radar will be three to four times bigger in area than
Raytheon’s Sea Based X-Band radar 240 ft. wide X 390 ft. long X 280 ft.
high . It will be the largest X-band system Raytheon has built, says Barry
Alexia, head of business development for the Advanced Concept Technology
Group, and will be twice as big as the ground-based Pave Paws,
Raytheon’s largest UHF radar. The ISIS radar will combine X-band and
UHF, and be a major departure from previous large arrays in more than
size. Bonded to the hull of an airship cruising at 65,000 ft., the radar
will flex more than if in a ground installation, creating challenges for
data processing, control and calibration. Darpa Defense Advanced Research
Projects Agency and its industry partners are also pushing the technology
envelope in hull material, propulsion and power generation, says ISIS
program manager Tim Clark. But the keystone is the radar, with designs
coming from Raytheon Space and Airborne Systems and Northrop Grumman
Electronic Systems. Clark wants to develop a dualband radar aperture with
an average weight, including operating DEFENSE ADVANCED RESEARCH PROJECTS
AGENCY Darpa envisions an airship covered with photovoltaic cells to feed
the solar-regenerative power system. The cutaway shows an active-array
radar antenna sheet bonded to the interior walls. electronics, of 2 kg.
4.4 lb. per square meter of aperture. The current state of the art for a
spacebased radar aperture is about 20 kg. per square meter, he says. The
power requirement is 5 watts or less per square meter on receive. A
go/no-go decision is planned for the spring of 2008. Contractors making
the cut will have until late 2010 or early 2011 to develop an aperture for
a three-month flight test. Radar performance is a function of power and
aperture. Airborne radars typically rely more on power because there’s
no room for big antennas on planes. But as aperture grows, so does
performance for search, track and fire control, while power requirements
decrease. The ISIS radar’s power needs will be small enough that it
won’t require a cooling system. In fact, it will have heating issues.
The solution is to run the radar all the time to keep it warm, Clark says.
With nominal winds, the power needed to run the radar and to move ISIS is
the same. But Clark says the fully regenerative fuel-cell system—the
first of its kind for this application and environment—must also have
surge capacity to hold station when winds reach 100 kt. and propulsion
requires 95% of power. Lockheed Martin Astronautics has reportedly beat
the threshold requirement of 400 watts for every kilogram of the power
system, including solar arrays, hydrogen fuel cells and storage tanks,
months ahead of a July-August deadline, and wants to double that. Darpa
believes ISIS will provide better radar capability than anything currently
available and be a boon to all of the services. For the U.S. Air Force, an
ISIS airship loitering over or near a battlefield will act like a combined
Joint Stars/AWACS aircraft. ISIS can tag along with carrier battle groups,
tracking airborne threats, especially sea-skimming anti-ship missiles. The
Army could use it to detect cruise missiles, something it is pursuing with
aerostats. Norad and Northcom may also be interested in ISIS for
cruise-missile defense and border applications. The radar will be able to
see aircraft, cruise missiles and other airborne threats up to 600 km. 373
mi. away and simultaneously paint ground targets—even individuals— out
to 300 km. The idea is to use the UHF function for broad searching and
zero in on interesting targets with the X-band. Thanks to the antenna’s
massive aperture, the UHF band, which can penetrate foliage while looking
for ground targets, will have enough resolution to spot vehicles on a
tree-lined road. ISIS will also be able to download images directly into
theater almost in real time. Using a fraction of the antenna, Clark says,
it is possible to drive a T3 data link down to a PDA 300 km. away,
allowing even lower-echelon commanders to see what ISIS sees. ■
www.aviationweek.com/dti 12 DEFENSE TECHNOLOGY INTERNATIONAL MARCH 2007
http://www.aviationweek.com/dtiTable of Contents for the Digital Edition of Defense Technology International - March 2007ContentsAround the WorldScience WatchTech WatchSwift BoatsFill 'em UpBuddy SystemLight ArmsWho Goes ThereDrones Down UnderPower PlayReady To RollTailor-MadeStrong SuitsShowtimeBird's Eye ViewMicro UAVs Power Up With Novel FuelsThe NetCutting EdgeOn the RecordIn ReviewInsightDefense Technology International - March 2007http://www.nxtbook.com/nxtbooks/aw/dti0908http://www.nxtbook.com/nxtbooks/aw/dti0708http://www.nxtbook.com/nxtbooks/aw/dti0608http://www.nxtbook.com/nxtbooks/aw/dti0508http://www.nxtbook.com/nxtbooks/aw/dti0408http://www.nxtbook.com/nxtbooks/aw/dti0308http://www.nxtbook.com/nxtbooks/aw/dti0108http://www.nxtbook.com/nxtbooks/aw/dti1207http://www.nxtbook.com/nxtbooks/aw/dti1107http://www.nxtbook.com/nxtbooks/aw/dti1007http://www.nxtbook.com/nxtbooks/aw/dti0707http://www.nxtbook.com/nxtbooks/aw/dti0607http://www.nxtbook.com/nxtbooks/aw/dti0507http://www.nxtbook.com/nxtbooks/aw/dti0407http://www.nxtbook.com/nxtbooks/aw/dti0307http://www.nxtbook.com/nxtbooks/aw/dti0107http://www.nxtbookMEDIA.com